The present invention relates in general terms to clutches, particularly for motor vehicles, and relates more in particular to the part of these clutches, commonly referred to as the clutch mechanism, which, itself constituting a unit assembly, is, in this form, designed to be fitted onto a plate, known as the reaction plate, after the insertion of a clutch plate in order to constitute such a clutch.
Stated in general terms, such a clutch mechanism includes a first generally annular part, known as the cover; a second generally annular part known as the pressure plate, which is connected for rotation with the cover by linking means which allow it to be displaced axially with respect to the latter; and axially acting resilient means, which, by bearing against the cover, act axially on the pressure plate in a direction tending to urge said pressure plate away from said cover.
The present invention particularly concerns the case where the linking means which link the pressure plate to the cover so that they rotate together are made up by elastically deformable leaf-springs which, individually or in sets, are fixed to the cover at one of their ends and at the other end are fixed to the pressure plate.
Such leaf-springs may, for example, extend substantially tangentially to a circumference of the clutch assembly.
Alternatively, they may extend substantially radially with respect to the axis of the clutch assembly.
Concerning the resilient means acting in the axial sense which operates between the pressure plate and the cover, these may, for example, be constituted by a peripheral portion, forming a Belleville or cup-shaped spring washer of a third annual part known as the diaphragm, the central portion of which is split up into radial fingers for the control and release of its said peripheral portion.
Generally speaking, it is desirable in clutch mechanisms of this type to be able to limit the axial travel which the pressure plate is able to undergo when acted on by the resilient means acting in the axial sense, which exert a force thereon.
This is the case, notably, during the time when such a clutch mechanism is being stored, prior to its assembly onto a reaction plate, since, if the pressure plate which is then not provided with countersupport by such a reaction plate via a clutch plate, were not then to have limited axial clearance with respect to the cover, this could result in deterioration of the linking means connecting it to the cover, particularly when these involve, as mentioned above, simple leaf-springs only exhibiting moderate strength in the axial sense.
This is the reason why the usual practice is to associate stop means with the pressure plates which are adapted to retain it in the axial sense after a determined length of axial travel with respect to the cover.
Such an arrangement, which has been known for some considerable time, is notably described in the French Patent filed under No. 77 05555 on Feb. 25, 1977 and published under U.S. Pat. No. 2,342,427.
In this French Patent, the stop means employed are made up by circumferential extensions of the leaf-springs which connect the pressure plate for rotation with the cover, and which, in practice, comprise in this case leaf-springs arranged substantially tangentially to a circumference of the assembly.
However, if such a design provides the advantage of allowing these stop means to be fixed to the cover using the same fixing means already used to attach the leaf-springs thereto, it makes it necessary, firstly, to fix these leaf-springs to the cover then onto the pressure plate, in order to assemble this clutch assembly, which complicates the latter.
Moreover, it makes it necessary to provide, in order to carry out such fixing, large passages in the peripheral edge of the cover, which has a detrimental effect on the rigidity of the latter.
Moreover, it is only really suitable in mechanisms designed to be attached onto a relatively flat reaction plate, and, consequently, only to mechanisms in which the cover is hollow, and not, inversely, to mechanisms in which said cover is relatively flat.
Moreover, it renders reconditioning and repair after first use of the mechanisms concerned difficult to carry out or even impossible, such reconditioning involving the cover as well and no longer just the pressure plate itself.
Finally, it can in practice only be applied to mechanisms in which the leaf-springs connecting, in rotation, the pressure plate to the cover can only be mounted in one sense.
Stated in other terms, a clutch assembly which is thus equipped is only able to operate correctly in one sense of rotation only, which, in an expensive fashion, makes it necessary to provide clutch mechanisms which are adapted to operate in one direction of rotation and in the other, and to carry out separate manufacturing runs.
In West German Patent application filed on Feb. 22, 1979 under No. P 29 06 863, one particular embodiment provides stop means which make use of arms which, independently of the cover, extend radially in order to cooperate with a transverse shoulder on the pressure plate.
However, in this West German Patent application, firstly, the arms thus used are fixed to the cover by means other than those used to attach thereto the leaf-springs providing the connection, in rotation, of the pressure plate to said cover, which complicates the practical embodiment of the assembly, and, secondly, they project at the internal periphery of said pressure plate thus decreasing the amount of space available in the axial sense for the clutch plate.
Moreover, these arms act on the side of the pressure plate corresponding to the periphery of smallest diameter thereof, and consequently at a relatively remote region, in the radial sense, from that at which the diaphragm moreover acts, which is not favourable to their effectiveness nor to their operating life.
In French Patent No. 1,580,169 stop means are provided which also employ at least one arm, which, independently of the cover, is fixed thereto by fixing means connecting to said cover the leaf-springs which connect the pressure plate to the cover for rotation therewith.
However, this arm cooperates with the rear face of the pressure plate, in order words with the face thereof which is most remote from the cover.
Such an arrangement, which has been designed for use in a clutch mechanism with a relatively flat cover is not suitable for use in all types of clutch mechanisms, and notably in those having a hollow cover.
Moreover, as it acts in the axial sense, it can bring about difficulties in respect of the axial sides of the assembly.
Finally, the Z-shaped configuration which practice requires the arm(s) employed to possess, may be somewhat difficult to achieve.
The present invention, stated in general terms, has as its object an arrangement which provides, in an advantageous fashion, a compromise between the previous arrangements, whilst at the same time avoiding the disadvantages of these, and which is advantageously adapted to all types of clutch mechanisms.